The present invention relates to a planetary gear, in particular for a wind power plant.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Modern wind power plants barely differ from one another externally. The differences lie substantially in the design of the gears which are provided between the rotor and the generator in order to convert the low rotational speed of the rotor hub into a higher rotational speed for the generator. For large plants, gear ratios of 1:100 are common. In order to produce such high gear ratios generally multi-stage gears are used. A combination of planetary gear stages and spur gear stages are typically used in common drive designs, wherein an obliquely toothed planetary gear is frequently used in the first high-torque gear stages, for a compact construction, whilst an obliquely toothed spur gear is used in the adjacent high performance stage.
The rotor shaft and/or rotor hub is connected to the planetary carrier of the first stage. The planetary carrier is mounted in two positions on axially opposing sides of the planet gears—i.e. on the drive side and on the output side of the gear stage—in the gear housing and drives the planet gears. Alternatively, mounting on one side is also possible. The ring gear is fixedly connected to the gear housing, resulting in a circulating motion of the planet gears in the gear mechanism. The torque is transmitted from the planet gears to the sun gear which is connected via an external spline to the planetary carrier of the second stage. The operation of the second planetary stage is identical to that of the first stage. In the last gear stage a further speed change is carried out by the spur gear driven by the sun gear of the second stage, so that a speed change is carried out from an initially low rotational speed of the rotor shaft at high torque to a high rotational speed of the generator shaft at low torque.
In conventional planetary gears and planetary-spur gears for wind power plants, rolling bearings are primarily used in order to mount the planet gears in the planet gear carrier and the planet gear carrier in the gear housing.
Hydrodynamically operated plain bearings are also occasionally used. Known plain bearing materials which are used here are, for example, white metals with alloy components and bronze alloys. Generally, plain bearings in industrial applications are designed with a lubrication gap of approximately 15 to 20 μm relative to the diameter in the operating point. At least 5 Mpa is set by the bearing manufacturer as the permissible mean dynamic pressure for white metal.
The use of plain bearings, however, is relatively rare. The reasons for this are the transient operating conditions which frequently prevail and the extremely low sliding speeds which temporarily occur, with the plain bearings being subjected to extreme stress at the same time. Conventional plain bearings are primarily used in conditions where high to very high rotational speeds are present. As a result, usually rolling bearings are almost exclusively used for bearing points in wind turbine gear mechanisms.
Irrespective of whether rolling bearings or plain bearings are used, attempts have been made to avoid operation in mixed friction conditions by lubrication measures and thus to keep the wear at the bearing points as low as possible. The measures which have to be taken for the lubrication and cooling of the gear components, in particular in the region of the bearing points, however, are cost-intensive.
In order to supply the planet gear bearings with lubricant, lubricant channels are formed in the planetary carrier axles, lubricant being supplied thereto via a lubricant supply channel formed in the planetary carrier. The lubricant supply channel is connected in turn via a slide bush to a lubricant channel which, in particular, axially penetrates the wall of the gear housing. The slide bush is formed in an annular groove which is formed in the front face of the planetary carrier on the output side. The slide bush has a central connecting channel which connects the lubricant supply channel in the planetary carrier to the lubricant channel in the housing wall. To this end, the slide bush is held fixedly in terms of rotation on the housing and the planetary carrier is rotatable relative to the slide bush. To this end, the radial wall surfaces of the annular groove and the radial wall surfaces of the slide bush in contact therewith are configured with corresponding tolerances. In other words, the outer diameter of the slide bush and the inner diameter of the annular groove are adjusted so as to form an exact fit with each other and in the same manner the outer diameter of the annular groove and the inner diameter of the slide bush form an accurate fit. The realization of two accurately adjusted dimensions both on the inner face and on the outer face of the slide bush and on the inner face and on the outer face of the planetary carrier is difficult to implement.
It would therefore be desirable and advantageous to provide an improved planetary gear to obviate prior art shortcomings and to simplify a supply of lubricant to the planet gear bearings.